In Karlsruhe on 19 June 1804, Wilhelmine married her maternal first cousin Louis, Hereditary Prince of Hesse-Darmstadt (1777–1848).

The union proved to be unhappy due to Louis's extramarital affairs, and they separated after the birth of their three older children.

In 1820, she acquired Schloss Heiligenberg, where Baron August von Senarclens de Grancy (1794–1871) was the chamberlain, and they started an affair.

Her last four children were believed to have been fathered by Senarclens de Grancy, although they were recognized by Grand Duke Louis II as his own.

Her descendants include Emperor Nicholas II of Russia (1868–1918) and his wife Empress Alexandra Feodorovna (1872–1918), last emperor and empress of Russia, her great-grandchildren; King Felipe VI of Spain (born 1968), the incumbent sovereign of Spain, her great-great-great-grandson; and King Charles III of the United Kingdom (born 1948), the incumbent sovereign of the United Kingdom, her great-great-great-grandson.